1. Field of the Invention
The present invention relates to a liquid crystal display panel and a liquid crystal display device in which an orientation film is formed on a substrate surface, and more particularly relates to a liquid crystal display panel and a liquid crystal display device in which a polysilicon thin film transistor is formed as a switching device.
2. Description of the Related Art
In recent years, liquid crystal display devices that make use of the energy-saving, lightweight, and thin profile characteristics are used in small equipment such as projector devices and mobile phones, and in large equipment such as notebook computers and liquid crystal televisions, and the use thereof is rapidly increasing.
Liquid crystal display devices display images by applying voltage to a liquid crystal layer sealed between two substrates disposed facing each other, and control the contrast by varying the transmission ratio of light that passes through the liquid crystal layer, that is, by using the liquid crystal layer as a light control element. An example of this method is a simple matrix drive for driving a liquid crystal device in which a liquid crystal layer is sandwiched between a scanning electrode group in which a plurality of scanning electrodes are arrayed in the form of stripes, and a signal electrode group in which a plurality of signal electrodes are arrayed in the form of stripes in the direction orthogonal to the array direction of the scanning electrode group, and voltage is applied to the portions where the scanning electrodes and signal electrodes intersect in a plan view. However, a simple matrix drive has a problem in that the display quality is poor because the number of scan lines is limited.
For this reason, an active matrix in which the pixels are provided with switching devices is conventionally widely used in a liquid crystal display device in order to improve the performance of the simple matrix drive described above. A thin film transistor in which amorphous silicon is used is ordinarily used as the switching device. Since the amorphous silicon thin film transistor is easily and inexpensively formed on a substrate with a large area, it is used in a variety of fields.
However, amorphous silicon thin film transistors have a problem in that the mobility of the electric charge is poor, and when amorphous silicon is formed as the switching device, the drive circuit for driving the thin film transistor must be mounted in the vicinity of the display panel. This presents an obstacle when a liquid crystal display device is miniaturized, and it is difficult to apply a liquid crystal display device obtained using an amorphous silicon thin film transistor to a mobile telephone or other small equipment that needs to be made thinner and more lightweight.
In view of the above, liquid crystal display devices that use a polysilicon thin film transistor with a higher charge mobility than amorphous silicon are becoming more widely used. Polysilicon thin film transistors are effective for narrow framing in which the peripheral portion of the display area is made smaller because peripheral drive circuits are formed on the same substrate.
FIG. 1 is a diagram that schematically shows a conventional liquid crystal injection method. Manufacturing this type of liquid crystal display device commonly entails laminating a drive substrate 102 and an opposing substrate (not shown) by way of a seal member 103, as shown in FIG. 1, and thereafter using the capillary phenomenon to inject liquid crystal material between the two substrates from the liquid crystal injection inlet 105 formed in the seal member 103. In order to improve the video performance of the liquid crystal display device, however, there is a trend toward narrowing the interval, that is, the gap between the drive substrate 102 and the opposing substrate. VA (vertical alignment) liquid crystal which has a very low injection speed is coming to be widely used in place of TN (twisted nematic) liquid crystal which is conventionally used. For this reason, there is a problem in that time is required when the liquid crystal is injected between the drive substrate 102 and the opposing substrate.
To solve this problem, a liquid crystal display device has been proposed in prior art in which the portions other than the display area have an interval (gap) between the substrates that is greater than that of the display area, and a liquid crystal injection inlet is provided in the portion where the gap is wide (refer to Japanese Laid-Open Patent Application No. 10-123571, for example). FIG. 2 is a plan view that schematically shows the liquid crystal display device described in Japanese Laid-Open Patent Application No. 10-123571. FIG. 3A is a cross-sectional view along the line F-F shown in FIG. 2, and FIG. 3B is a cross-sectional view along the line G-G shown in FIG. 2. In FIGS. 2, 3A and 3B, the constituent components of the opposing substrate 101 and the wiring disposed on the drive substrate 102 are not shown in order to simplify the diagram. The liquid crystal display device 100 described in Japanese Laid-Open Patent Application No. 10-123571, as shown in FIGS. 2, 3A and 3B, is configured so that the following components are disposed facing each other via a resin seal member 103: an opposing substrate 101 on whose surface are formed a light-blocking film (not shown), a transparent electrode (not shown), an orientation film (not shown), and other components, and a drive substrate 102 on whose surface are formed a signal line (not shown), a scan line (not shown), a switching element 125, a protective film 122, a smoothed film 123, a pixel electrode (not shown), and an orientation film 124. A liquid crystal layer 104 is held between the opposing substrate 101 and the drive substrate 102.
The seal member 103 is formed so as to surround the periphery of the display area 106, and a liquid crystal injection inlet 105 for injecting liquid crystal is disposed in a portion thereof. A recess 107 is formed in the area that serves as the liquid crystal injection inlet 105 and in the area between the display area 106 and the seal member 103 in the surface of the drive substrate 102. The recess 107 is extended from the liquid crystal injection inlet 105, is fashioned so as to surround the display area 106, and is formed by removing the protective film 122 and the smoothed film 123, for example. Thus, the liquid crystal display device 100 has a recess 107 formed on the periphery of the liquid crystal injection inlet 105 and the display area 106, the amount of liquid crystal injected per unit of time is increased by widening the gap rather than the display area 106, and the liquid crystal is caused to permeate from the external periphery of the display area 106 toward the interior thereof to reduce the liquid crystal injection time.
However, the above-described prior art has the following problems. The liquid crystal molecules must be oriented in a fixed direction in order to drive the liquid crystal layer as a light control element. For this reason, a rubbed orientation film is disposed in the portion of the surface of the opposing substrate and the drive substrate that is in contact with the liquid crystal layer. The orientation film is commonly formed by a method in which printing is performed using an orientation plate on which a convexity is formed in the portion for forming the orientation film. Specifically, a material (orientation material) for forming an orientation film is applied to the surface of the orientation plate, and the orientation material is transferred to the surface of the drive substrate. In this manner, when the orientation film is formed by printing on a flat substrate surface, the thickness of the film at the edges of the orientation film thus formed may increase because the orientation material tends to gather at the edges of the convexity of the orientation film.
FIG. 4 is a cross-sectional diagram showing the thick film portion of the orientation film. If the orientation film 114 has a thick film portion, as shown in FIG. 4, the cell gap in this portion becomes narrow, that is, a narrow gap portion 116 is formed, and the effect thereof is difficult to obtain even if a recess 107 is formed in the surface of the drive substrate 102, and time is required for liquid crystal injection. Thus, the liquid crystal display device described in Japanese Laid-Open Patent Application No. 10-123571 has a problem in that when an orientation film is formed by printing, a thick film portion is formed on the edges thereof and the injection speed of the liquid crystal is reduced.
Since the voltage-transmission characteristics of the liquid crystal varies in accordance with the thickness of the orientation film and the thickness of the liquid crystal layer, when a thick film portion is formed on the orientation film 114, as shown in FIG. 4, the thickness of the orientation film 114 and liquid crystal layer 104 becomes nonuniform, and fluctuations occur in the voltage-transmission characteristics of the liquid crystal. Display nonuniformity occurs as a result. Thus, when the orientation film 114 has a thick film portion, thin film transistors and other switching elements 115 must be disposed so as to avoid the thick film portions in order to prevent display defects from being created by the presence of the thick film portions. For this reason, the conventional liquid crystal display device shown in FIG. 4 has a problem in that the frame width L becomes wider by an amount equal to the thick film portion, and narrow framing is difficult.
FIG. 5 is a cross-sectional diagram showing the state of the orientation film after rubbing treatment, on which a thick film portion is present. When a thick film portion is present on the orientation film 114, as shown in FIG. 5, there is a problem in that dust 118 generated from the thick film portion spreads to the display area 106 when the orientation film 114 is rubbed, and display defects are created.
In the same manner as in the liquid crystal display device described in Japanese Laid-Open Patent Application No. 10-123571 shown in FIGS. 2 and 3, when the protective film 122 and smoothed film 123 are removed from portions other than the display area 106 in order to form a recess 107, the wiring (not shown) for the feeding voltage that drives the switching elements 125 and the transparent substrate 121 composed of glass or the like are exposed. When the wiring is exposed, for example, the wiring is liable to be damaged when the orientation film 124 is subjected to the rubbing treatment step, the spacer dispersion step, and other steps. Also, when the transparent substrate 121 is exposed, impurities from the transparent substrate 121 are dispersed in the liquid crystal layer 104, and display defects are liable to occur. When a recess 107 is formed by removing the protective film 122 and the smoothed film 123 in this fashion, there is a problem in that reliability is reduced.
When the configuration shown in FIG. 2 is applied to a liquid crystal display device formed with peripheral drive circuits further inward from the seal member 103, there is a problem in that the drive circuits are liable to be damaged in the rubbing treatment step, the spacer dispersion step, and other steps, because the smoothed film formed on the peripheral drive circuits must be removed.